StarDate: Eta Carinae

FROM THE UNIVERSITY OF TEXAS McDONALD OBSERVATORY, AS HEARD ON KCBS RADIO WEEKDAYS @ 9:52 A.M., 7:35 P.M. & 2:52 A.M

STARDATE 6/16/2014: One of the most intriguing star systems in the galaxy may be about to get a lot more interesting. There are a signs that it may be building up to a big eruption — a possible prelude to an even bigger blast.

Eta Carinae is too far south to see from the United States. And it’s barely visible even from southern skies. Yet that hasn’t always been the case. In the 1840s, the system flared brilliantly. For a while, it was the second-brightest star in the night sky.

The system is a binary — two stars bound by their gravitational pull. The smaller star is probably about 30 times as massive as the Sun. But its companion is truly extraordinary — a monster that may be more than a hundred times the Sun’s mass.

It was this star that caused the brilliant flare-up. It staged a mammoth eruption, blasting out enough material to make 10 stars as heavy as the Sun. That material soon cooled and condensed to form a cloud of dust. The cloud looks like a big peanut with a tutu around its middle.

The dust from the outburst absorbed much of the system’s light, so it faded from view completely. In recent decades, though, the system has begun to brighten again. In part, that’s because the cloud is expanding, so the dust is more spread out, allowing more starlight to shine through. But that doesn’t account for all of the system’s brightening. Some models do account for it though, and they suggest that another eruption could be on the way. More about that tomorrow.